Soil CO2 emissions as a proxy for heat and mass flow assessment, Taupō Volcanic Zone, New Zealand. (18th December 2014)

• Record Type: Journal Article
• Authors: Bloomberg, S.; Werner, C.; Rissmann, C.; Mazot, A.; Horton, T.; Gravley, D.; Kennedy, B.; Oze, C.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 15:Number 12(2014:Dec.)
• Page Start: 4885
• Page End: 4904
• Publication Date: 2014-12-18
• Subjects: Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1002/2014GC005327
• Languages: English
• ISSNs: 1525-2027

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high‐resolution measurement of carbon dioxide flux (φCO<sub>2</sub>) and heat flow at the surface to characterize the mass (CO<sub>2</sub> and steam) and heat released to the atmosphere from two magma‐hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taupō Volcanic Zone, New Zealand, include over 3000 direct measurements of φCO<sub>2</sub> and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO<sub>2</sub> emission rates (ΣCO<sub>2</sub>) of 441 ± 84 t d<sup>−1</sup> and 124 ± 18 t d<sup>−1</sup> were calculated for Rotokawa (2.9 km<sup>2</sup>) and for the crater floor at White Island (0.3 km<sup>2</sup>), respectively. The total CO<sub>2</sub> emissions differ from previously published values by +386 t d<sup>−1</sup> at Rotokawa and +25 t d<sup>−1</sup> at White Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO<sub>2</sub> emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal‐sourced CO<sub>2</sub> emission (constrained using stable isotopes) with reservoir H<sub>2</sub>O:CO<sub>2</sub> mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MW<sub>t</sub>) is 10 times greater than the White Island crater floor (22.5 MW<sub>t</sub>).</p> </abstract>